Carbon nanomaterials, which are nanosize carbon materials, are promising reinforcing materials, and metal-carbon nanocomposite materials can be manufactured by adding Mg and Al. The dimensions of carbon nanomaterials are reduced to the nanoscale, causing the materials to aggregate easily. In view of the above, a manufacturing method in which carbon nanomaterial is uniformly dispersed in Mg or another matrix metal is disclosed in Japanese Patent Application Laid-Open Publication No. 2006-44970 (JP 2006-044970 A).
The manufacturing method disclosed in JP 2006-044970 A is different from a manufacturing method in which a carbon nanomaterial is directly added to molten Mg. In other words, Si microparticles are deposited by vacuum deposition on the surface of the carbon nanomaterial. The Si-coated carbon nanomaterial is added to the molten Mg. Si demonstrates an anchor effect and facilitates bonding between the carbon nanomaterial and Mg. The fact that an Si-coated carbon nanomaterial is superior to a carbon nanomaterial can be evaluated based on wettability. This is due to the fact that particles of the material closely adhere to each other and the bonding properties improve as wettability increases.
FIGS. 11A and 11B show an evaluation of the wettability of a carbon nanomaterial and the Si-coated nanomaterial disclosed in JP 2006-044970 A.
The wetting angle is measured as shown in FIG. 11A when angle θ1 or θ2 is small, and as shown in FIG. 11B when one of the angles is large.
In FIG. 11A, an Si-coated carbon nanomaterial 102 is bonded by fusion to a substrate 101 (e.g., SKD61) made of steel by discharge plasma sintering, a small hole is formed in the center of the substrate 101, and the surface is polished. A vacuum pump 104 is used to form a vacuum inside a vacuum chamber 103, argon gas is subsequently supplied from an argon gas supply tube 105, and a nonoxidizing atmosphere is formed inside the vacuum chamber 103. Additionally, the interior of the vacuum chamber 103 is set to the same temperature as the molten Mg (700° C.). Next, molten Mg 107 is pushed up using a cylinder 106. The molten Mg 107 spreads on the top of the Si-coated carbon nanomaterial 102 and forms a dome. The wetting angle at this time is designated as θ1.
In FIG. 11B, an ordinary carbon nanomaterial 108 is placed on the substrate 101. The configuration is otherwise the same as in FIG. 11A, and the molten Mg 107 is substantially spherical. The wetting angle at this time is designated as θ2.
FIG. 12 shows a graph that compares wettability. Molten Mg has good wettability relative to an Si-coated carbon nanomaterial at a wetting angle θ1 of 42°. Molten Mg has poor wettability in relation to a regular carbon nanomaterial at a wetting angle θ2 of 157°. Consequently, vacuum deposition of Si microparticles on a carbon nanomaterial in advance is an effective technique.
The present inventors substituted molten Mg for molten Al and performed an experiment in which an Si-coated carbon nanomaterial was wetted with molten Al. At this point, the rolling angle was 154°, as shown at the right end of the graph. There was therefore no special significance to the vacuum depositing of Si microparticles on the carbon nanomaterial in advance. In other words, it was made apparent that an Si-coated carbon nanomaterial could not merely be added to molten Al, and a solution for this situation was necessary.